Maxima Function
ifs ([r1, ..., rm], [A1, ..., Am], [[x1, y1], ..., [xm, ym]], [x0, y0], n, ..., options, ...);
Implements the Iterated Function System method. This method is similar
to the method described in the function chaosgame, but instead of
shrinking the segment from the current point to the randomly chosen
point, the 2 components of that segment will be multiplied by the 2 by 2
matrix Ai that corresponds to the point chosen randomly.
The random choice of one of the m attractive points can be made with a non-uniform probability distribution defined by the weights r1,...,rm. Those weights are given in cumulative form; for instance if there are 3 points with probabilities 0.2, 0.5 and 0.3, the weights r1, r2 and r3 could be 2, 7 and 10.